Reinforced paper



April 16, 1963 c. HARMON x-:T AL 3,085,906

REINFORCED PAPER Filed July 27, 1959 2 Sheets-511991l 1 ATTORNEY April 16, 1963 c. HARMoN ET AL 3,085,906

REINFORCED PAPER Filed July 27, 1959 2 Sheets-Sheet 2 I l l I l l l l /0 20 30 40 .50 60 70 0 90 /00 /f' ey/m///f ATTO R N EY States This invention relates to unified paper backings for various uses, more particularly to flexible paper backings unified by impregnating the paper with rubbery binder solids until the paper is internally strengthened and is particularly suitable for use as a backing material for products such as pressure-sensitive adhesive masking tapes and the like.

Backings of this type, particularly those which must be used in flexible pressure-sensitive adhesive tapes, must possess a number of important physical properties to a high degree. These include flexibility, delamination strength, tensnile Strength, 'and various other properties such as edge tear strength, elongation, abrasion resistance wet and dry, and the like. Various attempts have been made to build all of these properties into paper backings which are particularly suitable for pressure-sensitive adhesive tapes and similar products. Backings of this general type are described in United States Patents 2,726,967; 2,848,105; and 2,848,355. All of these patents describe the problem in some detail and provide various ways for unifying the backing 'sheet by impregnating it with a rubbery binder material, as well as different ways of improving the binder and enhancing the effectiveness of the fiber binder relationship.

In products of this general type, it is highly desirable to improve delamination strength and tensile strength, as Well as flexibility. For instance, it has been common in the manufacture of backings Afor pressure-sensitive adhesive tapes of vthe type described in the above patents to impregnate the starting paper web with 80 yto 100` percent or more of a rubbery binder material by weight of the dry paper fibers. Normally, this involves saturating" the paper web, ie., substantially filling in the interstices formed between the interlacing paper fibers with the binder solids. There is a tendency of such papers either to become stiff or too rubbery, either of which may be undesirable for various applications.

Accordingly, it is an object of this invention to provide an improved unified paper backing which possesses tensile strength and delamination strength to a high degree and in addition possesses a high degree of flexibility.

Another object of the invention is to provide such a backing which possesses these three properties to a high degree and which contains a comparatively low proportion of rubbery binder solids, i.e., normally not above 50 percent of the weight of the paper fibers, although as high as 70 or more percent of the binder solids may be employed for certain applications.

Still another object of the invention is to provide an improved unified paper backing for pressure-sensitive adhesive tapes, such -as masking tapes, which possesses improved tensile strength, delamination strength flexibility and openness when compared with prior art backings of the same general type, and yet contains a much lower percentage of rubbery impregnant solids.

A further object of the invention is to provide improved paper backings of the type described which are more economical than prior art backings of the same general type.

Other :and further objects of #the invention will be apparent from the following description and claims taken together with the drawings.

The backing of this invention comprises a web or network of moderately hydrated or substantially unhy- 3,085,90 Patented Apr. 16, 1963 drated woodpulp fibers, rubbery binder solids portions distributed substantially uniformly throughout the web, and a multiplicity of relatively large flexible and tough thermoplastic reniforcing members distributed substantially uniformly throughout the web in bonding relation l with the woodpulp bers. The woodpulp fibers are arranged in overlapping crossing relation with one another so as to define a multiplicity of minute interstices between them. The relatively large reinforcing members define a corresponding multiplicity of space `between the members in the web. The average distance across the spaces between the reinforcing members is considerably greater than the average distance across, or the size, of the relatively minute interstices between the woodpulp fibers so that several of these interstices generally are located in each of the spaces between the reinforcing members. The rubbery binder solids portions hold the woodpulp fibers together between reinforcing members.

The structure of the reinforced web product of this invention is determined to a large extent by the relative sizes lof the woodpulp fibers and the thermoplastic reinforcing members, and the relative proportions by weight -of these components in the web. The woodpulp fibers are relatively small when compared with the reinforcing members, i.e., the woodpulp fibers are in the range of about 0.04 to 0.4 mils in thickness and about 0.4 to 0.8 mils in width, and are less than 1A inch in length normally within the range of about to 240 mils, while the reinforcing members are in the range of l to 35 mils in cross dimension and may be as long `as an inch or more, depending upon shape factors such as their length-towidth ratio. For instance, if they are in the form of rods having a more or less circular cross section and a lengthto-width ratio of 2 to l, normally over l0 to l or more, their cross dimensions may fall within the range of about l to 5 mils; and they may be between about gg and l inch or `over in length, although rods below about 1A inch in length may be preferred. However, when the length-towidth ratio of the reinforcing members is decreased until length `and width become more nearly equal to each -other and the members are in the form of granules, the cross dimension of the reinforcing members may be between about 5 and 35 mils.

In a given product according to this invention, the sizes of the reinforcing members and the woodpulp fibers are of different orders of magnitude, i.e., the individual reinforcing members are at least about 5, preferably l0 or more, times larger in cross-sectional area than the individual woodpulp fibers. Thus, even if equal proportions of the woodpulp fibers and reinforcing members are used, the above-described relationship exists wherein the spaces between the reinforcing members 4are considerably larger than the interstices between the woodpulp fibers, and the binder solids portions form a multiplicity of bonds between the woodpulp fibers in the spaces between the reinforcing members. However, the reinforcing members and the binder solids are applied in the web in certain definite proportions which contribute to the desired structure. Normally, the over-all weight of the reinforcing members with respect to the dry woodpulp fiber solids falls within the range of about 5 to 30 percent, although as little as 2 or 3 percent and as much as 50 percent yof the reinforcing members by weight may be used with desirable results for certain applications. The range for the reinforcing members of 5 to l5 percent by weight is particularly preferred for products such as paper backed pressure-sensitive adhesive tapes such as masking tapes and the like. As mentioned above, the normal range for the rubbery binder solids portions, particularly for pressure-sensitive adhesive tapes and the like, is between about 20 to 50 percent by weight of the woodpulp fiber solids and reinforcing members, although binder solids may be 3 applied within the range of about 10 to 70 percent or more by weight on the same basis for particular applications.

When substantially unhydrated woodpulp fibers and fiexible and tough thermoplastic reinforcing members bearing the above-described size and weight relationship to one another are distributed in a web in the proportions by weight set forth above, the desired structure of the backing of this invention is obtained. In this structure, the spaces between the reinforcing members are considerably greater in size or cross dimension than the size or cross dimension of the interstices between the overlapping crossing woodpulp fibers.

The structure of the fabric of this invention will be explained and may be better understood by reference to the following drawings wherein:

FIGURE 1 is a schematic plan view of a paper web according to this invention as one embodiment may appear;

FIG. 2 is a schematic sectional view along the line 2 2 of FIG. 1;

FIG. 3 is a graph of tensile strength versus percent impregnation for a paper web according to Example V herein;

PIG. 4 is a graph of Gurley stiffness versus percent impregnation for the paper web of FIG. 3; and

FIG. 5 is a graph of delamination resistance versus percent impregnation for the paper web of FIG. 3.

`Referring to the drawings, relatively short and small woodpulp fibers 11 are arranged in overlapping crossing relation with one another so as to form a multiplicity of interstices 12 between them. The woodpulp fibers are bonded together by rubbery binder solids portions 13 distributed substantially uniformly throughout the web, as well as a multiplicity of relatively large rod-shaped fiexible and tough thermoplastic polymeric reinforcing members 14 distributed substantially uniformly throughout the web.

It is believed that the reinforcing members 14 may perform various functions in the web structure. First of all, each of the reinforcing members 14 bonds a large number of woodpulp fibers 11 which pass through or into contact with the member. As shown most clearly in FIG. 2, the individual reinforcing members 14 entrap a number of adjacent or contiguous woodpulp fibers 11 in the plane of the web and perpendicular thereto, or through the thickness of the web. The woodpulp fibers 11 are held firmly in the individual reinforcing members 1-4 since the woodpulp fibers passing through each member 14 are in contact with the material of the reinforcing member along a high proportion of the length of the woodpulp fibers 11.

The reinforcing members 14 define a multiplicity of spaces 15 between them; and the average distance across the spaces is considerably greater than the average distance across the interstices 12, or the size of the interstices, formed between interlacing woodpulp fibers 11. Thus, several of these interstices 12 generally are located in each of the spaces 15 formed between the reinforcing members 14.

In a sense, the web is interrupted by the reinforcing members 14 so as to form a multiplicity of web islands corresponding to the web areas in the spaces 1S between the reinforcing members 14, which are joined together by the reinforcing members. Continuing this analogy, the islands are formed by the woodpulp fibers 11 in the spaces 15 and the rubbery binder solids portions 13 which hold these fibers together to form a connected network structure. The reinforcing members 14 defining the islands may be compared to hinges between islands which provide elements of fiexibility scattered throughout the web structure. It is believed that the hinged island structure just described may contribute to the improved fiexibility of backings of this invention, although other factors such as the lower percentage of binder solids portions present and fiber orientation also may affect iiexibility.

While the exact reason for the improved delamination strength of backings according to this invention is not denitely known, it is possible to offer more than one possible explanation. For instance, as shown best in FIG. 2, it is believed that the binder members 14 act somewhat like large logs in a mill pond or marbles in a match box to cause certain of the woodpulp fibers 11 to become upended or more angularly disposed with respect to the plane of the web so that a fairly high percentage of woodpulp fibers have a component in the direction of the thickness of the backing. This should increase delamination strength, since it becomes necessary to tear more fibers to delaminate the web, as opposed to tearing fewer fibers and then separating laminar sections of the web. Another way of saying this is that the presence of the relatively large reinforcing members 14 causes a higher degree of woodpulp fiber orientation in the direction of the thickness of the web. This also may tend to increase the flexibility of the web.

It also is possible that a high percentage of this increased delamination strength may be due to the fact that the fiexible and tough reinforcing members l14, themselves, extend through a high proportion of the thickness of the web as illustrated in FIG. 2. Thus, in order to delaminate the backing, it is necessary to rip through a large number of the reinforcing members 14.

The increased tensile strength of backings according to this invention also may be due to the fact that the reinforcing members 14, themselves, possess considerable strength and act like the steel rods in reinforced concrete to add tensile strength to the web.

In forming backings according to this invention, it is preferred to distribute the reinforcing members in the web during the papermaking step. Normally, this step involves distributing the woodpulp fibers in a substantially nonhydrated or moderately hydrated state in water to form an aqueous slurry of woodpulp fibers and mixing the proper proportion of thermoplastic reinforcing members with the woodpulp fibers in the slurry until they are distributed substantially uniformly in the slurry and intimately intermingled with the woodpulp fibers. The slurry is then drained through some sort of collecting means for making paper such as a Fourdrinier wire, a drum screen, a hand sheet mold, or the like to form a paper web. After drying and pressing as is conventional in papermaking, heat and pressure are applied to the web containing the reinforcing members in such a way as to soften and preferably fuse the thermoplastic reinforcing members and press them through the thickness of the web so that they entrap a large number of woodpulp fibers. Temperature and pressure are controlled carefully so that the material of the reinforcing members does not iiow too freely and cause the members to lose their shape. `For instance, if temperature is too high, under certain pressures surface tension may cause the material in the reinforcing members to ball up; and of course if pressure is too high, it will squeeze the reinforcing members and fiatten them out to too great an extent. It is inevitable in this process that the reinforcing members be attened to a certain extent, and allowance can be made for this. Thus, the cross dimension of the reinforcing members in the resulting fabric may be as great as twice that of the rods or granules from which they are formed, although the increase in cross dimension due to the application of lheat and pressure during the bonding of the reinforcing members normally is not this great.

After the bonds between the reinforcing members and the woodpulp fibers have been formed and the web has been allowed to cool to permit the bonds to become set, the rubbery binder solids may be applied thereto. Normally, this is accompiished by impregnating the web with an aqueous dispersion of a natural or synthetic rubbery latex, or by impregnating it with a natural or synthetic rubber composition deposited from solution in a volatile organic solvent. These methods are taught in United States Patents 2,726,967 and 2,236,527, respectively.

Woodpulps, the fibers of which are suitable for use in producing backings in accordance with this invention, include relatively long fiber kraft-type pulps, such as, Duracel pulp sold by the Canadian International Paper Company. The pulp may be either unbeaten (unhydrated) or slightly hydrated but not to the extent that it is not definitely fibrous in form. Generally speaking, it has a Schopper-Riegler freeness of at least about 600 cc. or more. Thus, Webs formed from the fibers of such a pulp are open and comprise fibers overlapping and crossing one another and forming myriad relatively minute interstices between them. As mentioned hereinbefore, the individual woodpulp fibers are in the range of about `0.104 to `0.4 mil in thickness and about 0.4 to 0.8 mil in width, and generally are less than about 1A inch, say about S0 to 240 mils, in length. From the above, it is apparent that the woodpulp fibers are somewhat flat, or ribbon like, in shape. They may be more or less straight or somewhat curled and kinked as may result from being subjected to treatment such as described in United States Patent 2,516,384 to provide curlated fibers.

The relatively flexible and tough thermoplastic reinforcing members of this invention preferably are selected from among a number of long-chain polymeric materials which form flexible and tough solid granules or rods. Nylon `6 comprising polycaprolactarn gives particularly good results when used as the material for the reinforcing members of this invention. Other materials, which may be employed for the reinforcing members, include Nylon -1\1 such as sold under the trademark Rilsan by Organico, S. A., of France, Saran, polyamides other `than `Nylons y6 `and l1, polyvinyl chloride, polyethylene, polyurethane, polystyrene, polyvinylidene cyanide, plasticized cellulose acetate, plasticized ethyl cellulose, and the like.

The size of the reinforcing members may vary over a wide range. If the reinforcing members are in the shape of rods, prior to fusing, they normally would fall within the range of about 6.5-100 denier, corresponding to about 0.0005-0004 inch in diameter prior to fusing for the flexible and tough thermoplastic materials of this invention, and 1,4,2 to 1 inch in length. Preferably, the rods would be between about and 60 denier, corresponding to about 00012-00034 inch in diameter prior to fusing, and in the neighborhood of 1A inch or less in length. If the reinforcing members of this invention are in the shape of granules, prior -to fusing, they normally would be of such a size that 7 0 percent of the granules would not pass through a 200 mesh screen. Preferably, the majority of the particles are of a size that would not pass through a 1100 mesh screen. This means that generally speaking the average granule size will be within the range of about 0.004-0015 inch in diameter prior to fusing. Rods and granules outside the indicated ranges may be used provided that they are at least about 5, preferably 10 or more, times larger in cross-sectional area than the woodpulp fibers with which they are used.

The rubbery solids portions may be supplied from various natural yand synthetic elastomeric materials, or mixtures of an elastomeric component with -a thermosetting component, such as are 4described in United States Patents 2,848,105 land 2,848,655. As mentioned hereinbefore, the elastomer, or elastomeric mixture, may be in the form of :an aqueous dispersion of a synthetic rubbery latex or a natural or synthetic rubber composition in solution in a volatile organic solvent. Suitable synthetic rubbery latices may comprise polymers of butadiene and other conjugated dienes and their homologues, and copolymers and tripolymers based thereon, vinyl chloride polymers, copolymers of vinyl chloride with other materials lsuchas vinyl acetate and vinylidene chloride, chloroprene rubber and various other similar elastomeric polymers. Copolymers of butadiene and unsaturated nitriles, such as yacrylonitrile and the like, have been found to be particularly suitable for this purpose.

`Before application to the fibrous web, the rubbery binder ysolids may be in the form of relatively small particles ranging in size from about 0.004 to 0.2 mil in cross section, preferably not `above about 0.04 mil, normally having a length-to-width ratio in the neighborhood of 1:1. As the rubbery binder is applied to the web formed by the woodpulp fibers 11 and the reinforcing members 14, the rubbery binder solids portions 13 yare formed between the Woodpulp `fibers. The rubbery binder material may remain in the form of the original relatively small latex particles in which it is deposited. However, as the amount of the rubbery binder in the web is increased, the original latex particles tend to'join one another and form an at least partially continuous rubbery matrix with the rubbery binder solids portions connecting the woodpulp fibers in the areas 15 between the binder members 14 being in the form of agglomerates which may be somewhat filmlike in character. As the concentration of the rubbery binder solids portions is increased, the Vdeposited binder material becomes less particle-like and more like a continuous matrix in nature.

Backings according to this invention have many uses. As mentioned hereinbefore, their qualities make them particularly suitable as backings for pressure-sensitive adhesive tapes, particularly pressure-sensitive adhesive masking tapes and the like. They also are suitable for pressuresensitive packaging, identification, labeling, patching or mending, splicing, strapping, bundling and decorative tapes and the like and similar tapes of a non-pressuresensitive nature. In addition to its use in tta-pes, backings of this invention are particularly useful in sandpapens, protective papers, and similar fibrous web materials wherein flexibility and toughness are required.

Normally, backing webs according to this invention have a basis weight between about 25 to 30 pounds; i.e., 480 sheets `24 inches by `36 inches weigh this amount. However, this invention is not limited to this range of weight. For instance, the flexibility and therefore the conformability of protective papers having a basis weight ybetween about `60 and I80 pounds may be increased substantially in accordance with this invention without detracting from other desirable properties. In the same way, sandpaper backings accor-ding to this invention may have 'a basis weight as high :as 150 pounds.

Various embodiments of reinforced papers in accordance with this invention Will be illustrated in the following examples.

Example I Dry. Dryy Weight, g. Percent Curlated Sunila Pulp 1. 275 Nylon 6 Rods 0.225 l5 The wet sheet is removed from the sheet mold with a blotter, pressed at 2.3 pounds per square inch, and dried. Then, it is bonded in a Carver press at 200 pounds per square inch pressure and 425 F. for l0 seconds. 'The finished sheet basis Weight (including the Nylon 6) is 28 'Z pounds -per ream (l ream=480, 24 inches x 36 inches). The bonded sheet is impregnated with a synthetic impregnant comprising a rubber latex and la synthetic resin curing agent in accordance with the following formulation 8 Example I in such a way that the percent impregnation is 45% with the following results:

g Delamlnation and then is dried and cured. The percent impregnation, Web containingresistencia, l based on the weight of the unimpregnated sheet, is 10.3%. Ouncllcll, ucl

io \r 1 t; 69.9. Ingredients Manufacturer Prnt NZIYYOHG 39 (average),

10 G d h 74.0

Ilglijigtitnilch El-. l .i Example IV t Dgfvzciiiiiicctii 0.5 A resin-bonded backing is made up using curlated Sunila pulp beaten to a Schepper-Riegler freeness of l 1 The following delamination results are obtained when l5 qut 8670 Cdc arid meh long wddemer ger fllnellt d disheet Containing i yion rois using e same proce'ure as escri e in comlgalred glflth a comparable Stan ar Example I in the following proportions to form a web no yon having approximately the same basis weight:

Dclamlnation W t mit v Dm Driy eb con a ing oulcsesplllcmh eig g. Percent Width Sunila Pulp 0. 75 50 15% Nylon n 38.4. Nylon 6 0' 75 50 No Nylon 6 16 (average). 25

c I t 'Ihe resulting sheet is bonded, impregnated with the same Delamination resistance is measured inthis and in all of formulation `in the Same manner, dried and cured as in the following examples in accordance with the test method Example I in such a way that the percent impregnation defined by I, R. Dunlap in Some Factors Affecting Ply is 14,5% with the following results; Adhesion in `Latex Saturated Papers, appearing in Tappi, Volume 40' No' 8 August l19 57 page 677 Delamlnatlon, Gurley Tensile, 1b./in.

Web eontaiuingoz./in. Stillness, of width Example Il mg./iii.

A similar resin-bonded backing is made up using un- 5o \I 1 C 1d t 23.5 1 .0. beaten Duracel pulp of the type described hereinbefore %l you Sigianliiiiate. 7 and Nylon 6 rods, of .the same type and Size as described N0 Nylon n 12.0 (averasel- 52 (vcrsl- 11.2 (avrasel in Example I, using the same procedure as for Example I in the fOllOWUg PYOPQI10I10 fOfm a Web having aPPTOXI- Gurley stiffness is measured by a standard Gurley stiffmaely the Same baSlS Welghtf ness tester using the standard test procedure recommended by W. and L. E. Gurley, Troy, New York, and is Dryy Dry, expressed in milligrams per inch of width. Tensile Weight, s. Percent strength is measured by la standard tensile break test.

Duracel Pulp 1.44 9G Example V Nylon 6 Rods 0- 06 4 45 A resin-bonded backing is made up using curlated M Sunila pulp beaten to a Schepper-Riegler freeness of the resulting sheet is bonded, impregnated with the same about 870 CC, and 1/16 inch, 60 denier per filament Nylon fofmulalloll lll the Same manner drled and, Cured as, m 6 rods and using the same procedure as described in Ex- Example in such a way that the percent impregnation ample I Iln the following proportions to form a web '1S 72% Wllll the followlllg results: 50 having approximately the same basis weight:

W Dela'mination Dry Drv 0b contammg* ouiiccsesltlrrlclich Weight', g. Percent width Sunila Pulp 1. 35 90 4% Nylon 5 51.6, Nylon 5 l5 l0 No N ylon 6 37 (average).

The resulting sheet is bonded, impregnated with the ExampIe III formulation used in Example I to four different percenty, l d ages of impregnation, and then dried and cured in the A. feslll'bollded bacllllg ls made ,lP l uslllg Cul al@ same manner as in Example I. That the resulting product Sllfllla Pulp beafenl 0 a SChOPPef-Rleglef ffeelless 0f possesses higher tensile strength and delamination resistabout 870 CC- alld l lllcll long l5 delllePel lllanlellt ance and lower stiffness than a comparable standard sheet Nylon 6 f0d5-llslllg the s ame Procedure as lll EXmPle I containing no Nylon 6 is illustrated in the graphs of ln lll@ followlllg Proportlns t9 form a web llavlllg aP 65 FIGS. 3, 4 and 5 for tensile strength, Gurley stiffness and proximately the same basis weight: delamination resistance, respectively, versus percent impregnation based upon the weight of the unimpregnated Dry, Dry, sheet. Weghhg. Percent Example V1 (iulp S118 Various handsheets are made up using curlated Sunila y a pulp 0f 870 cc. freeness and each of the bonding materials l set forth in the second table below using the same proce- The resulting sheet is bonded, impregnated with the same dure as in Example I. The bonding material in rod form formulation in the same manner, dried and cured as in and the Sunila pulp are Vapplied in the following propor- 9 tions to form a web having approximately the same basis weight:

10. unbeaten Duracel pulp containing 10.5% Nylon 6 rods. The rods are 1/16 inch long and 15 denier per filament. The nished sheet weight (including the Nylon 6) is 30 pry, Dry, pounds per ream (l reain=480 sheets, 24 inches x 36 Weight, g. Percent inches). The sheet is bonded by passing it twice between s 1 P I a IO-inch diameter pressure roller and a 4-foot diameter un' a 1.275 85 Bonmglfateal .225 heated drum at a speed of 25 feet per minute. The osur face temperature of the drum is approximately 450: F. A inch thick silicone rubber belt passing over the S'Iflhrgsuhtmzgoheetsne bonded m a. Crver Press 32.11? 10 pressure roller serves to equally -distribute the pressure the t S a at P0311 s pr guaeblmcbnfressmha a and prevent sticking to the pressure roll. Pressure is sup- .me rrgid rlsl tsh Ofvn m1 tin af 165x :nmlv' I t y ar plied at 60 pounds per square inch to two 6-inch diamlabg tg45 t 7(1) e nrmfutl o e maan? gas eplsll eter hydraulic cylinders at either end of the pressure rawusheet gveicherl roe l enllrdgc ed 'in eth Orsi e roller. The sheet makes contact with the heated drum manner as fOrCEXm la I vlth th follllwino reselta'me 15 about three inches before going through the pressure P e 1 e C u s' nip. In passing the sheet through the second time, the sheet is reversed so that the opposite side is in contact Leigh tipirioei' $195133?? gfengt, DI??? With the heated drum. The sheet is then impregnated F. oz./in with a latex impregnant of the following composition:

Polyethylene (Hyl'ax) 1A@ 17 266 69.2 79.2 Solids DyIleL- 1s 15 325 64- 6 67- 2 Material Supplier Compo- M6 15 365 572 6810 Percent Control (no rods) 46.5 30.5

Hycar OR 25 B. F. Goodrich 70,0 Naugatex 2740.-. Naugatuck Chemical 0o-... 17. 5 Example VII Marmix Marbond Chemical Co 10.0 Durez 14798 Durez Plastics Co 2.0 Handsheets are made up using curlated Sunila pulp Versene Dow Chemical Co 0.5 of 8170 cc. freeness and various bonding materials in granular form using the procedure of Example I in the Water iS added t0 give 30% total solids. fOHOWlUg Proportion? t0 form a Web having aPPlOXl- The impregnated sheet is dried and then cured for 60 mately the Same 03515 Welght seconds at 350 F. Physical properties of the impregnated and cured sheet when determined as described in Dry, Dry, the foregoing examples are: W ht, P t

elg g me Percent impregnation 52 Delamination resistance ounces/inch i 1. 25 85 isslllllldzinguiimeriai .213,5 i5 Tensile, pound/ inch of width 14 Elongation to break, percent 4 The resulting sheets are bonded in a Carver press for 10 40 The sheet is then kiiife-coated on one side with a nitroseconds at 200 pounds per square inch pressure at the cellulose solution to give a coating weight of 0.3 ounce temperatures shown in the table below. The particle per square yard. On the opposite side itis reverse-roll size distribution is also shown in the following table. coated with a 33% solids toluene solution of a pressure- Percentage of Particles Bonding Larger 9.8-13.8 7-9.8 5.9-7 4.1-5.9 2.9-4.1 Smaller Temp., than 13.8 mils mils mils mils mils than F. mils 2.9 mils Formvar 15/958 (polyvinyl formai) 365 17 25 18 6 10 4 20 Etiiyi Cellulose N-ioo 300 19 20 10 5 3 i3 30 Butvar 98 (polyvinyl butyral) 374 65 14 10 3 1 2 5 Cellulose Acetate PM 203 437 21 29 19 7 6 6 12 The bonded sheets are impregnated with the impregnant sensitive adhesive of the following composition to profOrIIlUle 0f Example I t0 dePGS beiWeeH abOUt 35 and vide a masking tape according to this invention which 45% 0f impfegnan based. 011 the Welght 0f the dfY Sheet possesses greatly improved eXibility and conformability: and are dried and cured in the same manner as for Ex- 6o S 1 d .t. t ample I, and delamination resistance is measured as de- Pale crepe rubber o 1 s compo lon Pergns b 'th the followin results: scribed a ove, wi g GRS 1022 51 Aluminum hydrate C 730 20.3 percent. Dililggn Piccolyte S115 32.4 Imprgnatwn 01111ce Per meh m-Tolylene diisocyanate 1.0 Amberol M88 4.1 1115/195S. .1bb

g Santovar A 0.8 riuiaises/ilszl- I ggg 101101 0-8 iii A tt 203 gnltlrgisnocfos 34.1 25.8 The dried weight of adhesive is 2.28 ounces per square yard. 1 Example VIII Example 1X i Rolls of pressure-sensitive tape are made using a resin-l The Peper 0f Example VH iS treated n accordance bonded backing material. The paper for the backing is Wlfh the method 0f Urlled States Patent NO- 2,524,245 made on a l2-inch experimental paper machine using 75 to increase its elongation to break and delamination re- Percent impregnation 51 Delamination resistance, oz./in. 56

Tensile, pounds/inch 12 Elongation, percent 25 Example X A resin-bonded backing is made up using curlated Duracel pulp, beaten to a Schopper-Riegler freeness of 875 cc. and Nylon 6 rods of the size described in Example I, mixed in the following proportions to form a web having approximately the same basis weight:

Dry, Dry, Weight, g. Percent Curlated Duracel 1. 35 90 Nylon 6 0. 15 10 A control backing is made containing no Nylon 6. The other sheets are impregnated with a solvent-base impregnant of the following solids composition:

Material Supplier Dry,

Percent Depolymerized rubber (DPR) H. V. Hardman 3. 09 High Viscosity DPR -d 56.18 Amberol ST 137 25. 77 Staybelite Ester #l Hercules Powder Co 12. 89 Zirex Newport Industries Ine.. 1. 03 Monsanto Chemical Co. 0.52 Shell Chemical Co 0. 52

The impregnant solids is adjusted with toluene to give approximately 90% impregnation in both papers. The impregnated backings are dried and cured 5 minutes at 350 F. and are then tested for physical properties in accordance with the foregoing examples to give the following results:

Percent Delamin- Stifness, Tensile,

Impreg. ation, oz. ing/in. l /in Nylon 6 90. 5 65. 6 24 4. 0 No Nylon 6 90. 2 38. 4 52 3. 5

The manufacturers product names and trademarks used herein shall identify the following substances and types of materials. Hycar 1502X426 is a butadieneacrylonitrile copolymer comprising about 67% butadiene and 33% acrylonitrile and is in the form of a latex, while Hycar OR 25 is a more general name for the same type of material. Latex 2001 is a copolymer of butadiene and styrene in a 50:50 ratio. Naugatex 2740 is a similar copolymer of butadiene and styrene. Marmix is a copolymer of butadiene and styrene with a high styrene content, say about 85 to 90 percent, while GRS 1022 is a butadiene-styrene copolymer with a low styrene content in the neighborhood of about 25%. Durez 14798 and Amberol ST 137 are heat setting phenol formaldehyde resins, and Amberol M 88 is a rosin modified phenol formaldehyde resin. Dynel refers to a high molecular weight copolymer of vinyl chloride and acrylonitrile with the latter being present in a relatively minor proportion. Versene is a trade name for the sodium salt of ethylene diamine tetraacetic acid. Piccolyte S 115 is a polyterpene resin. Santovar A is an alkylated polyhydroxyphenol, while Ionol is a ditert-butyldiparacresol. Staybelite Ester #l0 is a glycerol ester of hydrogenated rosin, and Zirex is a zinc resinate.

Having now described the invention in specific detail and exemplified the manner in which it may be carried into practice, it will be readily apparent to those skilled in the art that innumerable variations, modifications, applications, and extensions of the basic principles involved may be made without departing from its spirit and scope.

The invention claimed is:

l. A reinforced paper web comprising a continuous network of moderately hydrated woodpulp fibers less than about 1A inch in length, said fibers being arranged in overlapping crossing relationship with one another so as to define a multiplicity of interstices between them, a multiplicity of relatively large flexible and tough thermoplastic polymeric reinforcing members distributed substantially uniformly throughout the web in bonding relation with the woodpulp fibers, said reinforcing members being between about 1 and 35 mils in cross dimension and at least about five times larger in cross-sectional area than said woodpulp fibers and defining a multiplicity of spaces between said members, said woodpulp fibers being at least partially imbedded in said reinforcing members, and rubbery binder solids portions distributed substantially uniformly throughout the web, said solids portions forming a multiplicity of bonds between the woodpulp fibers in the individual spaces between the reinforcing members, the reinforcing members and the binder solids being present in the web in amounts ranging between about 10 percent binder solids and 50 percent reinforcing members and 70 percent binder solids and 2 percent reinforcing members based upon the combined dry weight of the woodpulp fibers and the reinforcing members.

2. A reinforced paper web according to claim 1 wherein said reinforcing members essentially comprise a longchain polymeric material.

3. A reinforced paper web according to claim 2 wherein said polymeric material is nylon.

4. A reinforced paper web comprising a continuous network of moderately hydrated woodpulp fibers less than about 1A inch in length, said fibers being arranged in overlapping crossing relationship with one another so as to define a multiplicity of interstices between them, a multiplicity of fiexible and tough thermoplastic polymeric reinforcing members distributed substantially uniformly throughout the web in bonding relation with the woodpulp fibers, said reinforcing members being at least about ten times larger in cross-sectional area than said woodpulp fibers and defining a multiplicity of spaces between said members, said woodpulp fibers being at least partially imbedded in said reinforcing members, and rubbery binder solids portions distributed substantially uniformly throughout the web, said solids portions forming a multiplicity of bonds between the woodpulp fibers in the individual spaces between the reinforcing members, the reinforcing members and the binder solids being present in the web in amounts ranging between about l0 percent binder solids and 50 percent reinforcing members and 70 percent binder solids and 2 percent reinforcing members based upon the combined dry weight of the woodpulp fibers and the reinforcing members.

5. A reinforced paper web comprising a continuous network of moderately hydrated woodpulp fibers less than about 1A inch in length, said fibers being between about 0.04 and 0.4 mil in thickness and between about 0.4 and 0.8 mil in width and being arranged in overlapping crossing relationship with one another so as to define a multiplicity of interstices between them, a multiplicity of flexible and tough thermoplastic polymeric reinforcing members distributed substantially uniformly throughout the web in bonding relation with the woodpulp fibers, said reinforcing members being between about l and 35 mils in cross dimension and at least about five times larger in cross-sectional area than said woodpulp fibers and defining a multiplicity of spaces between said members, said woodpulp fibers being at least partially imbedded in said reinforcing members, and rubbcry binder solids portions distributed substantially uniformly throughout the web, said solids portions forming a multiplicity of bonds between the woodpulp fibers in the individual spaces between the reinforcing members.

6. A reinforced paper web comprising a continuous network of moderately hydrated woodpulp fibers less than about 1A inch in length, said bers being arranged in overlapping crossing relationship with one another so as to define a multiplicity of interstices between them, a multiplicity of rod-shaped thermoplastic polymeric reinforcing members distributed substantially uniformly throughout the web in bonding relation with the woodpulp fibers, said reinforcing members being between about 1 and 5 mils in cross dimension and at least about five times larger in cross-sectional area than said woodpulp fibers and defining a multiplicity of spaces between said members, said woodpulp ibers being at least partially imbedded in said reinforcing members, and rubbery binder solids portions distributed substantially uniformly throughout the web, said solids portions forming a multiplicity of bonds between the woodpulp iibers in the individual spaces between the reinforcing members.

7. A flexible, high delamination strength pressuresensitive adhesive tape which comprises a reinforced paper backing web, and a pressure-sensitive adhesive layer on one side of said web, said web comprising a continuous network of moderately hydrated woodpulp bers less than about 1A inch in length, said fibers being arranged in overlapping crossing relationship with one another so as to deiine a multiplicity of interstices between them, a multiplicity of rod-shaped thermoplastic polymeric reinforcing members distributed substantially uniformly throughout the web in bonding relation with the woodpulp bers, said reinforcing members being between about 1 and 5 mils in cross dimension and at least about five times larger in cross-sectional area than said woodpulp iibers and defining a multiplicity of spaces between said members, said woodpulp `fibers being at least partially imbedded in said reinforcing members, and rubbery binder solids portions distributed substantially uniformly throughout the web, said solids portions forming a multiplicity of bonds between the woodpulp iibers in the individual spaces between the reinforcing members.

8. A flexible, high delamination strength pressuresensitive adhesive tape which comprises a reinforced paper backing web, and a pressure-sensitive adhesive layer on one side of said web, said web comprising a continuous network of moderately hydrated woodpulp fibers less than about 1A inch in length, said iibers being arranged in overlapping crossing relationship with one another so as to define a multiplicity of interstices between them, a multiplicity of iieXible and tough thermoplastic polymerio reinforcing members distributed substantially uniformly throughout the web in bonding relation with the woodpulp libers, said reinforcing members being between about 1 and 35 mils in cross dimension and at least about five times larger in cross-sectional area than said woodpulp fibers and defining a multiplicity of spaces between said members, said woodpulp fibers being at least partially imbedded in said reinforcing members, and rubbery lbinder solids portions distributed substantially uniformly throughout the web, said solids portions forming a multi-V plicity of bonds between the woodpulp iibers in the individual spaces between the reinforcing members.

9. A pressure-sensitive adhesive tape according to claim 8 wherein said reinforcing members essentially comprise a long-chain polymeric material.

10. A pressure-sensitive adhesive tape according to claim 9 wherein said polymeric material is nylon.

l1. A flexible, high delamination strength pressuresensitive adhesive tape which comprises a reinforced paper backing Web, and a pressure-sensitive adhesive layer on one side of said web, said web comprising a continuous network of moderately hydrated woodpulp fibers less than about 1A inch in length, said bers being arranged in overlapping crossing relationship with one another so as to define a multiplicity of interstices between them, a multiplicity of relatively large iiexible and tough thermoplastic polymeric reinforcing members distributed substantially uniformly throughout the web in bonding relation with the woodpulp fibers, said reinforcing members being at least about iive times larger in cross-sectional area than said woodpulp iibers and defining a multiplicity of spaces between said members, said woodpulp fibers being at least partially imbedded in said reinforcing members, and rubbery binder solids portions distributed substantially uniformly throughout the web, said solids portions forming a multiplicity of bonds between the woodpulp fibers in the individual spaces between the reinforcing members, the reinforcing members and the binder solids being present in the Web in amounts ranging between about 10 percent binder solids and 50 percent reinforcing members and percent binder solids and 2 percent reinforcing members based upon the combined dry weight of the woodpulp fibers and the reinforcing members.

References Cited in the file of this patent UNITED STATES PATENTS 1,848,732 Lfionne Mar. 8, 1932 2,880,112 Drclich Mal'. 31, y1959 FOREIGN PATENTS 572,962 Great Britain Oct. 31, 1945 708,622 Great Britain May 5, 1954 OTHER REFERENCES Hoch: Mechanics of Latex impregnation, TAPPI, vol. 42, No. 3, March 1959, pages 164-465. 

7. A FLEXIBLE, HIGH DELAMINATION STRENGTH PRESSURESENSITIVE ADHESIVE TAPE WHICH COMPRISES A REINFORCED PAPER BACKING WEB, AND A PRESSURE-SENSITIVE ADHESIVE LAYER ON ONE SIDE OF SAID WEB, SAID WEB COMPRISING A CONTINUOUS NETWORK OF MODERATELY HYDRATED WOODPULP FIBERS LESS THAN ABOUT 1/4 INCH IN LENGTH, SAID FIBERS BEING ARRANGED IN OVERLAPPING CROSSING RELATIONSHIP WITH ONE ANOTER SO AS TO DEFINE A MULTIPLICITY OF INTERSTICES BETWEEN THEM, A MULTIPLICITY OF ROD-SHAPED THERMOPLASTIC POLYMERIC REINFORCING MEMBERS DISTRIBUTED SUBSTANTIALLY UNIFORMLY THROUGHOUT THE WEB IN BONDING RELATION WITH THE WOODPULP FIBERS, SAID REINFORCING MEMBERS BEING BETWEEN ABOUT 1 AND 5 MILS IN CROSS DIMENSION AND AT LEAST ABOUT FIVE TIMES LLARGER IN CROSS:SECTIONAL AREA THAN SAID WOODPULP FIBERS AND DEFINING A MULTIPLICITY OF SPECES BETWEEN SAID MEMBERS, SAID WOODPULP FIBEERS BEING AT LEAST PARTIALLY IMBEDDED IN SAID REINFORCING MEMBERS, AND RUBBERLY BINDER SOLIDS PORTIONS DISTRIBUTED SUBSTANTIALLY UNIFORMLY THROUGHOUT THE WEB, SAID SOLIDS PORTIONS FORMING A MULTIPLICITY OF BONDS BETWEEN THE WOODPULP FIBERS IN THE INDIVIDUAL SPACES BETWEEN THE REINFORCING MEMBERS. 